1. Field of the Invention
This invention generally relates to a bicycle rear derailleur. More specifically, the present invention relates to a bicycle rear derailleur in which main components, such as inner and outer plate members, are made from lightweight metal or steel plates having relatively smaller areas to thereby decrease the amount of material used.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle as well as the frame of the bicycle. One component that has been extensively redesigned is the bicycle rear derailleur.
As shown in FIG. 2, a conventional bicycle rear derailleur 10 includes a bracket 11 fixed to a frame of a bicycle, a base member 12 supported by the bracket 11, a link mechanism 13 coupled to the base member 12 at one end thereof, a movable member 14 coupled to the other end of the link mechanism 13, an outer plate member 15 movably supported to the movable member 14 and an inner plate member 18 located inwardly of the outer plate member 15 for freely rotatably supporting a guide pulley 16 and a tension pulley 17 between the outer plate member 15 and the inner plate member 18.
Furthermore, in order to prevent a chain winding around the guide pulley 16 and the tension pulley 17 for driving rear sprockets from accidentally disengaging and hence falling off from the bicycle rear derailleur 10, a disengagement prevention portion 19 is often provided at a position near the guide pulley 16 or the tension pulley 17. The disengagement prevention portion 19 extends substantially across a gap between the outer plate member 15 and the inner plate member 18. Thus, the chain can be prevented from significantly disengaging from the guide pulley 16 or tension pulley 17. FIG. 2 shows an example in which the disengagement prevention portion 19 is provided near the tension pulley 17 of the bicycle rear derailleur 10.
As shown in FIGS. 2 and 3, the disengagement prevention portion 19 of the conventional bicycle rear derailleur 10 includes a first protruded portion 15a and a second protruded portion 18a. The first protruded portion 15a protrudes rearwardly and outwardly from a tail end of the outer plate member 15. The second protruded portion 18a protrudes rearwardly and outwardly from a tail end of the inner plate member 18 farther than the first protruded portion 15. Moreover, the second protruded portion 18a is bent such that a front end edge of the second protruded portion 18a is located very close to a front end edge of the first protruded portion 15a. Thus, the disengagement prevention portion 19 is formed substantially across the gap between the outer plate member 15 and the inner plate member 18.
In addition, various parts of the bicycle rear derailleur 10 are made from different materials depending on its required mechanical characteristics, such as wear resistance. In general, the bracket 11 is made from lightweight alloys and the link mechanism 13 is made from lightweight alloys or steel. The outer plate member 15 and the inner plate member 18 are generally made from metal plates of lightweight alloys or steel by punching with a punching machine.
The outer plate member 15 of the conventional rear derailleur 10 is formed with a shape as shown in FIG. 4 by punching a metal plate M1′ with a punching die (not shown) of a punching machine (not shown). However, since the outer plate member 15 of the conventional rear derailleur 10 is formed at the tail end thereof with the first outwardly protruded portion 15a protruding rearwardly so as to form a portion of the disengagement prevention portion 19, the overall width of the outer plate member 15 is relatively large. This arrangement prohibits a compact layout of the outer plate members 15 to be punched on the metal plate M1′. In other words, the portion of the metal plate M1′ that is not effectively used, and hence wasted is large. As a result, the manufacturing cost is high for this type of bicycle rear derailleur.
Likewise, the inner plate member 18 of the conventional rear derailleur 10 is formed with a shape as shown in FIG. 5 by punching a metal plate M2′ with a punching die (not shown) of a punching machine (not shown). However, since the inner plate member 18 of the conventional rear derailleur 10 is formed at the tail end thereof with the second outwardly protruded portion 18a protruding rearwardly so as to form a portion of the disengagement prevention portion 19, the overall width of the inner plate member 18 is relatively large, which prohibits a compact layout of the inner plate members 18 to be punched on the metal plate M2′. In other words, the portion of the metal plate M2′ that is not effectively used, and hence wasted is large. As a result, the manufacturing cost is high for this type of derailleur.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle rear derailleur that overcomes the above mentioned problems in the prior art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.